Shut off valve for chromatographic system



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SHUT oFF VALVE FOR cHRoMAToGRAPHIc SYSTEM Filed July 8, 1960 3 Sheets-Sheet 2 44 d |L` (j 46 f Q3 POWER d GAS asf 42 52 54 l 3g 33\F l l l l I I 2o A S I 'ro SAMPLE SAMPLE y VALVE GAS INVENTOR. M. E.RE|NEcKE BMX A TTORNE YS Feb. 19, 1963 M. E. REINECKE 3,077,766

SHUT OFF' VALVE FOR CHROMATOGRAPHIC SYSTEM Filed July 8, 1960 3 Sheets-Sheet 3 SAMPLE LOOP I3 A ,1' I4 ll CARRIERMQXJO COLUMN @VENTI-:D

/Il/ 9 ll/ 9c M/ 9b /l POWER GASj IO *lu* I I' AIR TO COLUMN 9 /H/ lo! {VEN-TED INVENToR.

M. E. REINECKE www? A TTORNEYS 3,tl77,766 SHUT OFF VALVE FOR CHRMA'IGRAPHHC SYSTEM Marvin E. Reinecke, Bartlesville, Ghia., assigner to Phillips Petroleum Company, a corporation of Delaware Filed July 8, 196i), Ser. No. 41,667 3 Claims. (El. 73-23) This invention relates to a shut-olf valve. In another aspect it relates to a chromatographic analyzer system employing a power iluid operated, shut-olf valve between a sample source and a power fluid-actuated sampling valve, for assuring size uniformity of the sample slugs passed to the sorption column. In one aspect it relates to a delayed pressure-release, shut-off Valve which completely closes off sample conduit flow at the end of a preset interval, or while the power fluid supply to the analyzer system is interrupted.

Chromatographic analyzer systems are increasingly employed in the monitoring of process streams to provide automatic process control. This is because certain features of process chromatography, such as specific measurement, high sensitivity, and simplicity of operation, make this type of analyzer very attractive for use in automatic process control. There are, however, some apparently inherent features of chromatography which have appeared to be obstacles in adapting chromatography to wide-spread use in process control.

One of these features is the problem of periodically directing a sample slug of constant size to the sorption columns. Slug size uniformity is required in order to enhance the comparability of the chromatograms from one sampling time to the next for a given. sample stream. This objective is hindered by the varying flow rates and fluid pressures of the sample stream passing from the process stream to the sampling valve, which fluctuations are often unavoidable in plant operations. Consequently, for reliability of analyzer readings, some means of assuring that a uniform amount of sample is being repeatedly carried to the sorption columns is required.

Moreover, when the power gas supply to the analyzer system fails, some means of automatically terminating the ow of sample lluid to the sampling valve, for as long as the shut down occurs, is desired. This latter feature is to prevent flammable, Vaporized hydrocarbon sample from continuously bleeding from the process stream and venting through the sampling valve exhaust, thereby increasing the explosion hazard. Also, While the sealing members of the sampling valve are inoperative due to power gas failure, sample gas is prevented from passing to the sorption columns in an uncontrolled volume, thereby loading the column adsorbent, and often requiring replacement thereof.

In accordance with the present invention, there is provided a delayed pressure-release, shut-off valve which can be positioned between a process stream and a sampling valve, usually in the sample supply conduit of a vapor phase chromatographic analyzer. The sample shut-off valve of this invention is used in cooperation with a pilot valve in controlling the operation of a fluid-actuated, sampling valve.

The shut-off valve is intermittently slowly opened and closed and during the time it is open the sample fluid passes unrestricted therethrough to the sampling valve and is vented therefrom through the sample exhaust line. When the pilot Valve switches the power gas stream to the opposite side of the sampling valve and said power gas no longer tiows to said sample shut-off valve the sample fluid now passes through the sample loop of the sampling valve prior to being vented. By the time the preset pressure is reached, the plunger of the shut-olf valve is once again seated, and no more sample `gas is flowing to the sampling valve, thus permitting the sample gas already in the sample loop to come to equilibrium conditions. When the pilot valve again switches the power gas stream back to the first side of the sampling valve, a stabilized amount of sample is swept from the sample loop to the sorption column by carrier gas passing thereto.

It is, therefore, an object of this invention to provide an improved, delayed pressure-release, shut-olf valve.

Another object is to provide a chromatographic analyzer system incorporating a delay pressure-release, sample stream shut-oif valve between a process stream to be.

analyzed and a sampling valve for assuring size uniformity of the sample slugs passing to the sorption column.

A further object is to provide a safety shut-off valve in the sample gas conduit which automatically terminates sample fluid flow in the event of failure of the power gas supply, but which becomes re-operative as soon as the power gas supply is restored.

A still further object is to minimize the presence of a combustible fluid mixture in a chromatographic analyzer system in the event of power gas supply failure.

A further object is to prevent loading of the sorption column adsorbent and replacement thereof due to failure of the power gas supply to the sampling valve of a chro-v matographic analyzer.

4Further objects and advantages of this invention will FIGURE 2 is a cross sectional elevation of a shut-oft' valve of this invention with the plunger seated, and the valve in the closed position;

FIGURE 3 is a schematic view of a portion of the chromatographic analyzer showing the cooperative method of operation of the sample shut-olf, pilot and sampling valves;

FIGURE 4 is a diagrammatic plan view of a daphragm sampling valve in one position of operation, corresponding to the first open position of the shut-off valve of this invention while being bled down to the closed position;

FIGURE 5 is a schematic view of a typical diaphragm sampling valve shown in a position of operation corresponding to FIGURE 4;

FIGURE 6 is a diagrammatic plan view of a diaphragm sampling valve in the alternate position of operation,l

corresponding to the second open position of the shut-off valve while it is Ibeing pressured to the fully open position, and;

FIGURE 7 is a schematic view of the typical diaphragm sampling valve shown in another position of operation corresponding to FIGURE 6.

Referring now to the drawing in detail, wherein like parts have been vdesignated by like reference numerals, and to FIGURE 1 in particular, wherein a power gas such as air, passes via conduit 7 to pilot valve 8. The

power gas stream is directed therefrom to the rst or second inlets of a fluid actuated sampling valve 9 via conduits 1t) and 11. While power gas is passing through conduit 10 to the sampling valve 9, the second side of valve 9 is being vented via conduit 11, pilot valve S, and pilot valve exhaust conduit 12. Conversely, when power gas is passing through conduit 11 from pilot valve S,

the lirst side of sampling valve 9 is being vented throughl conduit 10.

A carrier gas, such as helium or hydrogen, continuously Patented Feb. 19, 1963 enters the 'system via conduit 13, through sampling valve 9, conduit 14, and on to sorption column 16. A sample stream enters the system through conduit 17, passing through a preheater 18 to vaporize the sample stream, if necessary, through a shut-olf valve 19, via conduit 20 to sampling valve-9. When pilot valve 8 permits power gas to flow `to the first side of sampling valve 9, via conduit 10, gaseous sample is passing through 'sample loop 21 thereof, and isvbeing vented through sample exhaust conduit 22. Simultaneously, power gas is bleeding back from shut-off valve 19 through' conduit 23, having flow restrictor 24 therein, via conduit `11 to pilot valve S, being `vented therefrom by exhaust conduit 12. Restrictor 2'4 can be any conventional needle valve of suitable size. The gas bleed down time -from valve 19 to exhaust 1-2 can beexperimentally varied to give a desired time interval, merely by adjustment `of the size of theorifice of restriction `De1ayed pressure-release shut-olf valve 19 is `p; sitioned in'tconduit 17 downstream from preheater 1S.` Shut-off valve `19` is intermittently retained in the open position, during which time 'llu'id Isample passes unrestricted to sampling valve 9, and is -vented ,directly therefrom through-sample exhaust yconduit 22. Shut-off :valve 19 operates `iin cooperation with pilot valve 8, which also controls the operation of sampling valve 9. Pilot valve 8, in turn, is'controlled by programmer 25. Periodically, sample'tluid `is passed along l*by carrier gas, via conduit 14,110 fsorption column 16, where constituents of the sample to be identified and measured, are absorbed and adsorbed, tdepending `u'ponthe nature ofthe sorbent material. They are then selectively desorbedby the continuing Vflow offcarrier gas through column 16.

4"The sorption column efliuent passes through an analyzer, indicated as lthermal conductivity cell assembly 26 via conduit 27. The output Isignal from TC detector 26 is passed to a recording instrument (not shown), which `can be a conventional strip chart recorder. Part o f the carrier gas stream' is passed from conduit 13 via conduit 28 directly to the reference side of thermal conductivity cell 26, so as .to balance out the effect of the samplecharged carrier gas stream passing through the first side of detector 26.

Pilot va'1ve"8 is actuated by programmer 25, whichcan be operated by a time cyclev or other means. Fora detailed discussion of the design and manner of operation of a typical pilot valve to be used in conjunction withthis invention, see the cro-pending application of Emmerich Guenthen-SerialNo.v 858,997, filed December l1, 1959.

When pilot valve 8 is changed from the rst described position, `power gas is now directed'to th'e'second side of sampling valve 9, via conduit 11, land the carrier gas now passes therethrough to sample `lloop 21, collecting the sample slug trapped therein, 'andlcarryingthesame out of sample loop 21` to conduit'14. Thus, each time pilot valve 8 is'swit'ched to the'second position jof'operation, a measured sample is passed via conduit 14 through column 16. For a more detailed discussion of the design and manner of operation of la pneumatically-actuated, diaphragm sampling valve to be used in conjunction with this invention, s ee the co-pending `application of M. E. Reinecke, vand `D. V. Eckert, Serial No. 8,548, led February 15,1960.

In FIGURE 2, there is shown an elevation view in full section of the assembled, delayed pressure release, sample shut-off valve of this invention, generally designated 19. Shut-off valve 19 comprises a valve body 29, having a centrally disposed valve seat 30 on the upper surface thereof. A first passage means 31 is provided in valve body 29 communicating between sample gas inlet conduit 17 and an annular groove 32 in valve seat 30. Passage 31 is counterbored and threaded at its external end to receive therein Van inlet nut 33 for securably connecting conduit 17 to valve body 29. Valve body 29 is further provided with a second passage means 34 communicating between the center 36 of annular groove 32 and a sample gas outlet conduit 20 leading to sampling valve 9. Passage 34 is also counterbored and threaded at its external end and is adapted toreceive therein a connecting nut 37 for securably connecting conduit 20 to valve body `29.

Plunger body 38 is mounted adjacent to valve body 29 and is spaced therefrom by a semi-rigid diaphragm 39, composed of a material such as a thermosetting plastic, which is chemically inert and heat resistant. A preferred material for diaphragm 39 is 3 mils in thickness and made of Teflon (a polymer of tetralluoroethylene).

A valve plunger 41 is disposed in plunger chamber 42 and is sealably engageable with plastic disc 43, which is adjacent to diaphragm 39 in one position of operation. Cylindrical disc 43, preferably of Viton A (a copolymer of hexatluoropropylene and vinylidene fluoride) which will `not cold flow and is resilient, is positioned in chamber 42 between diaphragm 39 and plunger 41, to provide uniform pressure on diaphragm 39. `A compression spring chamber 44 is located adjacent to plunger chamber 42 and is spaced therefrom by a second diaphragm 46. A preferred material for diaphragm46 is Fairprene coated fabric which is formed by impregnatng synthetic elastomeric compositions on both sides of woven fabrics. These compositions may be made from many types and grades of koilresistant synthetic rubbers.

A compression spring 47 is disposed in spring chamber 44 adjacent to diaphragm 46. Spring 47 has sufficient tension, when transmitted through spring retaining disc 48, diaphragm 46, plunger 41, and plastic disc 43, to maintain the spring assembly in a seated position against diaphragm 39, thereby sealing communication between passages 31 and 34. An O-ring 49, surrounds .a channeled portion 4of plunger 41, and is in sealing contact with the walls of plunger chamber 42, in order to minimize the escape of power gas therefrom. A pressure-adjusting screw 51 is threadedly secured in the `external end of spring chamber 44, 'for varying the tension in spring 47, as desired.

A passage 52 `is vprovided in plunger body `38 communicating between power fluid conduit 23 from pilot valve 8 and plunger chamber 42. Power lluid, under greater than atmospheric pressure, is conducted to chamber 42, as desired. Passage 52 is countenbored and threaded at its external end to receive a connecting nut 53 for securably fastening conduit 23 to plunger body 38. A fourth passage 54 is provided in plunger body 38 communicating between the lower portion of plunger chamber 42 and an area external of said shut-off valve, which serves primarily as a pressure equalizing vent.

The tension desired in compression spring 47, which is controlled by adjusting screw 51, as described, is chosen so as to `be equal in pounds to the power gas pressure in chamber 42 at which plunger 41 is to be seated against disc 43. The available power gas pressure which can be transmitted to chamber 42 must exceed the preset tensionin spring 47, in order to be able to release plunger 41 from exerting a sealing force against disc 43 and diaphragm 39.

In FIGURE 3, there is shown a schematic View of a portion of the chromatographic analyzer system which incorporates the novel combination of valves of this invention, and will be employed in the detailed description of the method of operation of this system which follows.

In operation, when power gas is tlowing via conduit 11 to motor 11M of sampling valve 9, power gas is simultaneously flowing through conduit 23 and flow restrictor 24 therein, to actuate motor 19M of shut-off valve 19. This power gas pressure opposes the spring tension of spring 47 which normally biases shut-olf valve 19 closed. In actuality, the power gas pressure building up in plunger chamber 42 of FIGURE 2, will overcome the spring tension bearing on the opposite side of diaphragm 46 via retaining disc 4,8, lifting plunger 41 from spaanse' valve seat 30, permitting sample gas flow between conduits 31 and 34 across valve seat 36 under diaphragm 39. This, of course, permits sample feed from inlet conduit 17 to pass to sampling valve inlet conduit 2d. As the power gas has actuated motor 11M to close passages 9A, 9B, and 9C of sampling valve 9, sample gas enters valve 9 from conduit 26, iiows through passage 9D, and is Vented via conduit 22, having restriction 22R therein. Meanwhile, carrier gas enters valve 9 from conduit 13, transits passage 9F, then through sarnple loop 21, back through passage 9e, and out of valve 9 Via conduit 14 to sorption column 16. Plunger #il of Valve 19 will remain in the raised position until such time as the power gas pressure in plunger chamber 42 is released.

When programmer 25 directs pilot Valve 3 to switch positions, the power gas stream now flows only to motor 10M of sampling Valve 9, via conduit 10, and is no longer flowing to shut-off valve motor 19M via conduits 11 and 23. As the power gas has now actuated motor 16M to close passages 9D, 9E, and 9F of sampling valve 97, sample gas must enter through passage 9A, pass through the sample loop 21, back into passage 9B, and is vented from valve 9 via conduit 22, having restriction 22R therein. Meanwhile, carrier gas, enters from conduit 13, transits passage 9C, and passes directly therefrom to conduit 14 and thence to column 16.

Simultaneously, the power gas in motor 19M is bleeding 4back therefrom through liow restrictor 2d in conduit 23. The needle adjustment in the iiow restrictor can be adjusted to permit this bleed back to occur over a predetermined period of time, perhaps several seconds, down to a preset pressure. When this preset pressure, usually about equal to the spring tension, is reached, motor 19M is off and valve 19 is closed, that is, as shown in FlG- URE 2, plunger 41 is once again seated against disc 43, and thus diaphragm 39 is sealed against valve seat 35i. Thus, sample gas is no longer ilowing through shut-off valve 19 to sampling valve 9. This permits the iiuid sample already in sample loop 21 of valve 9 to achieve equilibrium conditions.

When pilot valve S again switches positions, power gas is again directed back to motor 11M of sampling valve 9 via conduit 11, and power gas once more flows thereto, reopening valve 19, rse-establishing sample flow from conduit 17 through conduit 29 to sampling valve 9, and through passage 9D thereof, directly to vent Via conduit 22. Meanwhile, a stabilized amount of trapped fluid sample is being swept from the sample loop 21 to sorption column 16, via conduit 14, by carrier gas now passing through the sample loop.

Thus, the shut-off Valve of this invention assures sample size repeatability by shutting of sample gas flow to the sampling valve just a few seconds before the sampling valves position is switched by pilot valve 3, during which interval the sample achieves pressure equilibrium, and `drives the sample slug trapped therein to column 16.

FIGURES 4-7 show, diagrammatically, the operation of a diaphragm sampling valve which can be operater advantageously by the sample shut-oil valve of this invention in conjunction with the previously described pilot valve. The sampling valve is usually operated by air as the power gas, although the controlling pilot Valve and sample shut-off valve can be operated by the carrier gas where it is the only power iiuid available.

The paths travelled by the gaseous sample and the carrier gas through sampling valve 9 and sample loop 21 thereof, are shown in FIGURE 4, which corresponds to the iirst open position of the shut-oii valve of this invention while being bled down to the closed position.

FIGURE 5 shows carrier gas passing through the passage 9C, and sample gas passing through the companion passages 9A and 9B. Power gas pressure is being apr 65 plied to the lower side of valve 9 via conduit 10, while the upper side is being vented through conduit 11.

When pilot valve 8 (not shown) switches the power gas to conduit 11, the diaphragms in the sampling valve reverse position, and the paths travelled by the gaseous sample and carrier gas through sampling valve 9 are shown in FIGURE 6. Carrier gas is in the initial stage of driving the trapped sample slug to column 14. The View in FIGURE 6 corresponds to a second, slightly open position of shut-off Valve 19 while it is being pressured to the fully open position.

FIGURE 7 shows sample gas passing through passage 9D of valve 9 while carrier gas passes through the companion passages 9E and 9F. Power gas pressure is being applied to the upper side of valve 9 through conduit 11, while the lower side thereof is being vented through conduit l0.

Although the valve `as described is applied to a chromatographic analyzer, it is not limited thereto but can be employed in any situation where a fluid-actuated, delayed pressure-relief shut-on valve is indicated. Reasonable variations and modifications are possible within the scope of this disclosure without departing from the Spirit and scope of the invention.

I claim:

l. A shut-off valve comprising, in combination, a valve body including a valve seat, a plunger body mounted adjacent to said valve body and spaced therefrom by a flexible iirst diaphragm, a plunger chamber in said plunger body, a valve plunger in said plunger chamber engageable with said first diaphragm adjacent said valve seat, a compression spring chamber adjacent said plunger chamber and spaced therefrom by a metal second diaphragm, a compression spring disposed in said spring chamber having sufficient tension to bias said plunger in a closed posi-l tion on said iirst diaphragm, a pressure adjusting screw threadedly disposed in the external end of said spring chamber for varying the tension in said spring as desired, iirst passage means in said valve body for communicating between a sample gas inlet conduit and an annular groove in said valve seat, a second passage means in said valve body communicating between the center of said annular groove and a sample gas outlet conduit leading to an external sampling valve, a third passage means in said plunger body disposed between said iirst and second diaphragm, for conducting a power fluid under pressure as desired to said plunger chamber, an O-ring slidably surrounding said plunger and in sealing contact with the walls of said plunger chamber, a fourth passage means in said plunger body for permitting the venting of any power gas from said plunger chamber that may leak by said O-ring, said shut-off valve being operable in one position to permit unrestricted flow of fluid sample from said first passage -rneans across said valve scat to said second passage means when said power gas pressure in said plunger chamber overcomes the opposing spring tension and lifts said plunger from sealing contact with said valve seat, and said shut-off valve in another position of operation preventing the tiow of sample gas therethrough when the tension of said spring exceeds the opposing pressure of said power uid in said plunger chamber and sealably seats said plunger against said valve seat.

2. In a chromatographic analyzer system, means for periodically passing a sample slug of uniform size to a sorption column therein comprising, in combination: a sampling valve having a sample loop of fixed volume; flexible diaphragm means within said sampling valve responsive to the application of power fluid pressure to two sides thereof to actuate said sampling valve between two positions of operation; a first conduit means connected to said sampling valve to supply a fluid sample to Said sampling valve; a shut-off valve disposed in said first conduit means; a second conduit means communicating between said sampling Valve and said column; a pilot valve; third conduit means communicating between a means communicating between said pilot valve and said exible diaphragm means; fifth conduit means communicating Ibetween said pilot valve and said exible diaphragm means; sixth conduit means communicating between said fifth conduit means and with said shut-o valve; diaphragm means in said shut-off valve responsive to said power iluid to open and retain open said shut-off valve, so long as said power fluidis being supplied to the same; biasing means in said shut-off valve to close the same when said power uid is removed from said valve; time cycle means operatively connected to said pilot valve to alternately switch said pilot valve between a tirst position of operation during a rst time interval and a second position of operation during a second time interval, said power gas ilowing thru said fourth conduit means during said rst time interval, pressuring said flexible diaphragm means while said power gas is bleeding down from said shut-oit valve via said sixth and fifth conduit means; said power gas owing thru said fth and sixth conduit means during said second time interval, pressuring said exible diaphragm means and also opening and maintaining open said shut-off valve; and a flow restriction means disposed in said sixth conduit means adapted for control of the bleed down time of said power tluid from said shut-oli valve, thereby closing said shutot valve after a predetermined third interval of time within said Vtime interval, whereby fluid sample in said sample loop is permitted to come to equibrium conditions 'before said sample loop is switchedinto a stream of carrier gas passing to said column.

3. In a chromatographic Vanalyzer system, means for periodically passing a sample slug of uniform size to a s orption column therein comprising, in combination: a `sampling valve having a sample loop of lixed volume; flexible diaphragm meanswithin said sampling valve responsive to the application of power tluid pressure to twoV `sides thereof to actuate said sampling valve between two positions of operation; `a rst conduit means connected to said sampling valve to supply a uid sample tosaid sampling valve; a shut-off valve disposed in said first conduit means; a .second conduit means communicating between said sampling valve and said column; a pilot valve; third conduit means communicating between a source of power uid and said pilot valve; fourth conduit means communicating between said pilot valve and said exible diaphragm means; fth conduit means communicating between said pilot valve and said flexible diaphragm means; sixth conduit means communicating between said fth conduit means and with said shut-olf valve; diaphragm means in said shut-olf valve responsive to pressure of said power fluid to open and retain open said shut-off valve so long as said power uid is supplied thereto; spring means in said shut-oi valve for biasing closed the same when power uid is released therefrom; and a ow restriction means disposed in said sixth conduit means adapted to delay the closing of said shutoff valve when said uid bleeds back through said sixth conduit; time cycle means operatively connected to said pilot valve to alternately switch said pilot valve between a rst position of operation during a rst time interval and a second position of operation during a second time interval, said power gas tlowing thru said fourth conduit means during said first time interval, pressuring said flexible diaphragm means while said power gas is bleeding down from said shut-od valve via said sixth and fifth conduit means; said power gas flowing thru said fifth and sixth conduit means during said second time interval, pressuring said flexible diaphragm means and also opening and maintaining open said shut-oft valve, thereby closing said shut-off valve after a predetermined interval of time, whereby uid sample in said sample loop is permitted to come to equilibrium conditions before Asaid sample i,S switched into a stream of carrier gas continuously passing to said column.

Gas Chromatography by D. H. Desty, published in London by Butterworths Scientific Publication, 1958. (Copy in Div. 36.)

Patent Noo 3VO77V766 February 19 1963 Marvin En Reinecke n the above numbered petthat error appears i nt should read as It is hereby certified that the said Letters Pete ent requiring correction and corrected below.

first occurrenceq insert line 28 after "saiol'H7 u' read e equilibrium met,

Column L line 29V for "equibrum Signed and sealed this lst day of October 1963 (SEAL) Attest:

ERNEST W, SWIDER. DAVID L. LADD Commissioner of Patents Attestng Officer 

2. IN A CHROMATOGRAPHIC ANALYZER SYSTEM, MEANS FOR PERIODICALLY PASSING A SAMPLE SLUG OF UNIFORM SIZE TO A SORPTION COLUMN THEREIN COMPRISING, IN COMBINATION: A SAMPLING VALVE HAVING A SAMPLE LOOP OF FIXED VOLUME; FLEXIBLE DIAPHRAGM MEANS WITHIN SAID SAMPLING VALVE RESPONSIVE TO THE APPLICATION OF POWER FLUID PRESSURE TO TWO SIDES THEREOF TO ACTUATE SAID SAMPLING VALVE BETWEEN TWO POSITIONS OF OPERATION; A FIRST CONDUIT MEANS CONNECTED TO SAID SAMPLING VALVE TO SUPPLY A FLUID SAMPLE TO SAID SAMPLING VALVE; A SHUT-OFF VALVE DISPOSED IN SAID FIRST CONDUIT MEANS; A SECOND CONDUIT MEANS COMMUNICATING BETWEEN SAID SAMPLING VALVE AND SAID COLUMN; A PILOT VALVE; THIRD CONDUIT MEANS COMMUNICATING BETWEEN A SOURCE OF POWER FLUID AND SAID PILOT VALVE; FOURTH CONDUIT MEANS COMMUNICATING BETWEEN SAID PILOT VALVE AND SAID FLEXIBLE DIAPHRAGM MEANS; FIFTH CONDUIT MEANS COMMUNICATING BETWEEN SAID PILOT VALVE AND SAID FLEXIBLE DIAPHRAGM MEANS; SIXTH CONDUIT MEANS COMMUNICATING BETWEEN SAID FIFTH CONDUIT MEANS AND WITH SAID SHUT-OFF VALVE; DIAPHRAGM MEANS IN SAID SHUT-OFF VALVE RESPONSIVE TO SAID POWER FLUID TO OPEN AND RETAIN OPEN SAID SHUT-OFF VALVE, SO LONG AS SAID POWER FLUID IS BEING SUPPLIED TO THE SAME; BIASING MEANS IN SAID SHUT-OFF VALVE TO CLOSE THE SAME WHEN SAID POWER FLUID IS REMOVED FROM SAID VALVE; TIME CYCLE MEANS OPERATIVELY CONNECTED TO SAID PILOT VALVE TO ALTERNATELY SWITCH SAID PILOT VALVE BETWEEN A FIRST POSITION OF OPERATION DURING A FIRST TIME INTERVAL AND A SECOND POSITION OF OPERATION DURING A SECOND TIME INTERVAL, SAID POWER GAS FLOWING THRU SAID FOURTH CONDUIT MEANS DURING SAID FIRST TIME INTERVAL, PRESSURING SAID FLEXIBLE DIAPHRAGM MEANS WHILE SAID POWER GAS IS BLEEDING DOWN FROM SAID SHUT-OFF VALVE VIA SAID SIXTH AND FIFTH CONDUIT MEANS; SAID POWER GAS FLOWING THRU SAID FIFTH AND SIXTH CONDUIT MEANS DURING SAID SECOND TIME INTERVAL, PRESSURING SAID FLEXIBLE DIAPHRAGM MEANS AND ALSO OPENING AND MAINTAINING OPEN SAID SHUT-OFF VALVE; AND A FLOW RESTRICTION MEANS DISPOSED IN SAID SIXTH CONDUIT MEANS ADAPTED FOR CONTROL OF THE BLEED DOWN TIME OF SAID POWER FLUID FROM SAID SHUT-OFF VALVE, THEREBY CLOSING SAID SHUTOFF VALVE AFTER A PREDETERMINED THIRD INTERVAL OF TIME WITHIN SAID TIME INTERVAL, WHEREBY FLUID SAMPLE IN SAID SAMPLE LOOP IS PERMITTED TO COME TO EQUIBRIUM CONDITIONS BEFORE SAID SAMPLE LOOP IS SWITCHED INTO A STREAM OF CARRIER GAS PASSING TO SAID COLUMN. 